The hypothesis being tested in this research project is that abnormalities that may play a role in the pathogenesis of the disease exist in the functional interactions of nonmalignant T cells in patients with leukemia. During the first two years of the project, we completed our studies on the phenotypic characterization of T-cell subsets from 40 patients with B-cell chronic lymphocytic leukemia (CLL) and studied the immunoregulatory functions to B-cell responses of purified T4-\and T8-positive cells from a number of patients with CLL. These studies revealed a wide range of T-cell defects in patients with CLL. Suppressor cells within the T4 population were observed in certain patients with CLL. Our objectives for the third year of the project are: (1)\to conclude our studies on the immunoregulatory properties of purified T4-\and T8-positivecells from patients with CLL and their interactions. A total of 20 patients will be studied for analysis of the population with suppressor function present in T4-positive cells from certain patients with CLL and determination if abnormal T-cell functions are associated with hypogammaglobulinemia and other clinical parameters of CLL; (2)\to study T-T cell interactions between T4-\and T8-positive cells from patients with CLL during proliferative and cytotoxic responses to allogeneic cells in MLC; and (3)\to study cell interactions between remission T lymphocytes and autologous leukemic cells from patients with acute lymphoblastic or myelogenous leukemia during generation of "autologous leukemia-specific cell-mediated cytotoxicity" in "three-cell"-type mixed lymphocyte cultures for determination of the lymphocyte subpopulations that exhibit proliferative and cytotoxic responses to autologous leukemic cells as well as the cell surface phenotypes of effector cells, and the nature of the cell surface antigens on leukemic cells that elicit proliferative and cytotoxic responses by autologous T lymphocytes. It is expected that these studies will improve our understanding of these lymphoproliferative disorders and permit the design of more rational approaches for therapeutic and prophylactic management of the disease. (IS)